1. Field of the Invention
The present invention generally relates to a touch system and a touch sensing method, in particular, to an optical touch system and a touch sensing method.
2. Description of Related Art
In recent years, due to the convenience and intuitiveness on controlling, touch electronic products are favored by consumers and have become the mainstream in the market. In the resistive touch screen, the capacitive touch screen and the rear projection touch screen that are conventionally used in the electronic products, the capacitive touch screen has the best touch-sensing performance, but the manufacturing cost of the capacitive touch screen is the highest as well. Further, with the increase of the size of the touch screen, the manufacturing cost is also increased, so the application of the capacitive touch screen is limited. To find an alternative for the capacitive touch screen, an optical touch screen employing an optical component for sensing touch positions has been proposed due to various advantages including low cost and high accuracy. Since the optical touch screen is more advantageous in a competitive market, it is also a choice for the large size touch panel.
In a conventional optical touch display, at least two optical modules each composed of an image sensor and a light emitting unit are disposed at suitable positions on periphery or corners of a screen, and reflection frames are disposed around the screen. The light-emitting units emit light toward the reflection frames and the reflection frames reflects the light, and the image sensors sense a brightness state of the reflected light to determine whether an object exists on the screen and calculate the position of the object. For example, when a user's finger (or other object) moves onto the screen, the position of the shadow caused by the finger obstructing the reflected light can be sensed by the optical modules, and a precise touch position of the finger can be calculated accordingly. Generally, two optical modules only can sense positions of two fingers on the screen. The number of the optical modules has to be increased while more touch positions of fingers are to be sensed. However, the added optical modules will be disposed at positions adjacent to the two optical modules or positions on the frames or corners opposite to the two optical modules, so that a “face to face” problem is happened to at least one of the optical modules. The details are explicated below. The disposing positions of the optical modules are positions without reflection frame (such as a gap between two reflection frames). Therefore, when the light-emitting unit of one of the optical modules (hereinafter “optical module A”) emits light toward the adjacent and opposite reflection frames, another optical module (hereinafter “optical module B”) located in the gap of the opposite reflection frames is unable to generate a reflected light with the same intensity as that of a light reflected by the reflection frames. Thus, the image sensor of the optical module A will determine the intensity of the reflected light at the optical module B is not enough and a dark point exists correspondingly, which is mistaken as a touch object (such as a user's finger) obstructing the reflected light. Thus, the optical touch system is unable to recognize the real touch object and confusing situation happens, and it is hard to determine how many touch objects exist and the precise position of each touch object.